1. Field of the Invention
The present invention relates to a control unit for adjusting the angle of rotation of a camshaft in relation to the angle of rotation of a crankshaft, in an internal combustion engine.
2. Background Information
The present invention relates to a control unit for adjusting the angle of rotation of a camshaft in relation to the angle of rotation of a crankshaft, as is known from DE 41 35 378 for example.
In internal combustion engines, the crankshaft drives one or more camshafts via a primary drive, which is realized as a chain, toothed belt, upright shaft or as a series of gear wheels. To do this, a camshaft wheel, via which the primary drive drives the camshaft, is fixed to each camshaft and is realized corresponding to the primary drive as a pulley wheel or sprocket wheel, for example. This always involves a gear ratio reduction of the angular rotation of the crankshaft, in which 720xc2x0 angular rotation of the crankshaft is converted into 360xc2x0 angular rotation of the camshaft.
In order to ensure that the working cycle of the internal combustion engine runs precisely, and to maintain the control times required for exact combustion, the crankshaft, primary drive and camshaft are manufactured to very tight tolerances.
Thus it is advantageous to eliminate the fixed relation between the crankshaft and the camshaft, for example for speed-dependent adaptation of the control times of the valve clearance, and to allow the camshaft to lead or lag the crankshaft. This is achieved in a simple manner by means of a control unit which displaces the camshaft in relation to the camshaft wheel. The combustion chambers of the internal combustion engine are opened and closed correspondingly earlier or later by the valves as the camshaft turns during the working cycle. This provides an opportunity of further improving the running characteristics of the internal combustion engine so as to save fuel and, above all, to reduce exhaust emission.
Such a control unit is known from German Patent Publication DE 41 35 378, corresponding to U.S. Pat. No. 5,311,846 (Mxc3xcller et al.), wherein the camshaft of an internal combustion engine is displaced in relation to the crankshaft by means of a hydraulic control unit. The hydraulic control unit includes a wobble plate pump which permits controlling the hydraulic pressure required to displace the camshaft.
The disadvantages of a hydraulic control unit lie in the extensive space occupied by the pump arrangement and the hydraulic chamber system, the arrangement""s susceptibility to faults, and the relatively high manufacturing costs.
The object of the invention is to provide a control unit for adjusting the angle of rotation of the camshaft in relation to the angle of rotation of the crankshaft, which requires little space, is inexpensive to manufacture, and which is very safe in operation.
This task is solved in accordance with the invention by the combination of the following features. According to the invention there is provided an apparatus for adjusting an angle of rotation of a crankshaft driving said camshaft, said apparatus comprising a drive transmission (6) between said camshaft and said crankshaft, said drive transmission including at least one transmission wheel (2) for driving said camshaft by said crankshaft, said drive transmission further comprising at least one rotatable wobble plate (3) and a wobble drive (5) for driving said at least one rotatable wobble plate (3), said at least one rotatable wobble plate (3) comprising at least one wobble drive member positioned for driving said transmission wheel in response to an operation of said at least one wobble drive (5) to thereby control a transmission ratio between said camshaft and said crankshaft through said at least one rotatable wobble plate.
In this case, with an internal combustion engine, camshaft and crankshaft are connected to each other via a primary drive which drives the camshaft via a camshaft wheel connected to the camshaft. Here, the wobble plate mechanism is arranged between the camshaft wheel and the camshaft.
A wobble plate is attached to one side of the wobble plate mechanism, an actuator which drives the wobble plate is also arranged on this side.
A further development of the invention provides for the wobble plate on the opposite side to the actuator to have two rotating gear rings. Here, the first gear ring of the wobble plate engages in a gear ring acting on the camshaft wheel, and the second gear ring of the wobble plate engages in a gear ring acting on the camshaft.
An alternative development of the invention provides for a rotating gear ring to be arranged on each side of the wobble plate. Whereby the gear ring on one side of the wobble plate engages with a gear ring acting on the camshaft wheel. The gear ring formed on the other side of the wobble plate engages with a gear ring acting on the camshaft.
The displacement of the angle of rotation of the camshaft in relation to the camshaft wheel results from the intermeshing gear rings of the wobble plate and of the camshaft wheel and/or the intermeshing gear rings of the wobble plate and of the camshaft having different numbers of teeth.
In the above described embodiment the wobble plate has an axial angle in relation to the camshaft. The effect of this axial angle is that only an angular segment of the gear rings of the wobble plate engages with the gear rings of the camshaft and the camshaft wheel. The size of the angular segment within which the gear rings intermesh is a function of the axial angle of the wobble plate in relation to the camshaft.
A particular simple embodiment of the invention provides for the actuator to directly drive the wobble plate bearing the gear rings.
An alternative, somewhat more complex, embodiment of the invention provides for the actuator to directly drive a further wobble plate, and the further wobble plate transmits the wobbling motion via connecting rods in sliding bearings to the wobble plate bearing the gear rings.
Means are provided which limit the displacement of the camshaft in relation to the crankshaft to a maximum displacement of the camshaft of xc2x140 degrees.
In a final development of the invention, means are provided which realize a displacement of the camshaft in relation to the crankshaft of 0 degrees if the actuator fails.